DC testing above 5kV of field aged XLPE cables generally increases water tree growth and reduces service life.Studies carried out on DC high voltage testing of XLPE cables now conclude that.HV test on XLPE cables already in service or previously energizedĮxcept for New Cables, Testing at Voltage greater than 5.0KV is not permitted Where HV cable circuits are cut and joined to new circuits, sheath testing must be carried out on the existing old circuit prior to joining to the new cable.For cables after repairs, the resistance must not be less than 10 meg-ohms.
The integrity of the outer sheath shall be checked after cables have been buried by an insulation tester (Megger) at 1000 Volts.In new cables, values of greater than 100 mega ohms are required. Fault finding can often be very difficult. Values between 1.0 and 10 meg-ohms may not indicate damage in a single location. Values below 0.5 meg-ohms (500 kΩ) can indicate sheath damage.The purpose of the test is to determine soundness of the outer polyethylene sheath against water ingress, mechanical damage and termite attack.Outer Sheath Insulation Resistance (Screen wire test) Where the test is performed on the wire screens, they shall be disconnected from earth.The test may be conducted on either the wire screens or the aluminum conductors. 240 Volt mains frequency is not acceptable for the performance of this test. This test shall be performed with an instrument designed for the purpose.The correct phasing of all HV circuits shall be checked at all positions where the HV cables have been terminated.In any overhead or underground network the overall resistance to earth Shall be less than 1 ohm prior to connection to the existing network.ġ1 KV AND 33 KV XLPE Cables : Phasing Test.In any overhead or underground network the earth resistance at any point along the length of a LV feeder is to have a maximum resistance of 10 ohms prior to connection to the existing network.A typical instrument would be the earth “Megger” type and taking into account the resistance values of the test leads.The instrument used for this measurement should have a resolution to the second decimal point in the 0 to 5 ohm range.Any difference greater than this may indicate a loose or dirty connection and will require further investigation. The difference between the readings of each phase conductor and the neutral for each individual test shall not be greater than 10% of each other.In a fused service pillar the bottom row of fuses bases must be the point at which the test is undertaken as that is the furthest extent of the network. (2) Undertake a continuity test at every point where there is a service provision or open point.(1) At the transformer firmly bond all 4 conductors together.The test shall be carried out as follows: For loop LV systems, a continuity test shall be carried out on each LV circuit to ensure that all bolted connections are complete and adequate.The neutral conductor shall be connected to the earth stake for this test.Ĭontinuity Test (resistance of bolted connections):.Mains frequency voltage of 240 Volts is not acceptable for this test. The correct phasing of all LV circuits shall be checked at all positions where the LV cables are terminated into fuse bases and where any LV cable is run from point to point.At the conclusion of LV insulation resistance testing, the neutrals must be connected to the earth stakes.The instrument used for this measurement shall have a minimum resolution of 10 meg-ohms on the 0 to 500 meg-ohm range.The minimum insulation resistance to earth or between phases shall be 100 meg-ohms.Cables shall be tested for insulation resistance with an insulation tester (i.e.J68 Comments Low Voltage and High Voltage Cable Testing Low Voltage XLPE Distribution Cables: Insulation Resistance:
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